1. Field of the Invention
The present invention relates to a feeding device and an image forming apparatus.
2. Description of the Related Art
An image forming apparatus capable of double-side printing usually includes a discharge unit that discharges a sheet and a switchback unit that switches back a sheet for double-side printing. If each of the discharge unit and the switchback unit is configured to function with both a feed roller group including a feed roller that feeds a sheet and a roller group including a roller rotatable along with the feed roller, the discharge unit and the switchback unit cannot be operated at the same time.
If the switchback unit is configured to function by using three roller groups including a feed roller group provided with a feed roller that feeds a sheet, a first roller group provided with a roller rotatable along with the feed roller, and a second roller group rotatable along with the feed roller being in contact with the first roller group, it is possible to discharge a sheet by the first roller group, and at the same time, to switchback a feeding direction of another sheet for double-side printing by the second roller group. Therefore, the number of sheets that can be printed per unit time increases compared with that using two roller groups of the feed roller group and the single roller group.
When performing one-side printing, a sheet with an image on one side is discharged to a sheet catch tray by the feed roller group and the first roller group. On the other hand, when performing double-side printing, a sheet with an printed image on one side is conveyed toward the sheet catch tray by the feed roller group and the second roller group, and by reversing rotational direction of the feed roller group before discharging the sheet, the sheet with the printed image on one side is switched back toward a double-side printing path.
At the same time, the feed roller group and the first roller group feed the sheet with a printed image on both sides toward the sheet catch tray to discharge the sheet. At this time, a sheet guide is not usually arranged in a direction of the sheet catch tray in the second roller group so that a discharged sheet can be taken out easily. With this configuration, the sheet being conveyed toward the double-side printing path and the sheet being discharged come closer to each other.
An image forming apparatus for realizing the above functions is disclosed in Japanese Patent Application Laid-Open No. 2005-112533 and Japanese Patent Application Laid-Open No. 2005-194089. The image forming apparatus includes a driving source which can switch rotational direction of the feed roller group between forward and backward and a switching guide that switches the sheet feeding direction toward a switchback feeding path for double-side printing.
Furthermore, some image forming apparatuses perform a switching operation using a plurality of gears, while an oscillating gear that oscillates with the switching operation is provided between a driving unit and the feed roller. The sheet feeding direction is switched by oscillating the oscillating gear at each switching operation.
Moreover, other image forming apparatuses include the first roller group having a projected portion in an annular manner at one end of the roller in the first roller group to corrugate the sheet to be discharged to impart stiffness on the sheet. Therefore, it is possible to prevent drooping-down of the discharged sheet near the first roller group and its overlapping and rubbing with the sheet catch tray and already-discharged sheet. Thus, the sheet being fed to the sheet discharge tray does not rub, and thereby damage or stain on the image formed on the sheet can be prevented. Furthermore, a recess portion is provided with a projected portion on the end of the first roller to have a projection and recess shape on a circumference of the first roller. By hooking a rear end of the sheet by the projected portion and rotating the first roller group, the rear end of the sheet is fed out with momentum so that the discharged sheet does not drop or bend before the sheet catch tray or interfere with a subsequent discharged sheet.
In a feeding device that feeds a sheet in a first direction by a feed roller group provided with a plurality of feed rollers and a first roller group rotated along with the feed rollers, and also feeds another sheet in a second direction opposite to the first direction by a second roller group rotated along with the feed roller, the following problems often occur. When the sheets are conveyed in the first direction and the second direction at the same time and if the sheets come close to each other, the sheet discharged from the feed roller group and the first roller group hardly droops because it is fed with stiffness, but the sheet fed toward the sheet catch tray from the feed roller group and the second roller group easily droops thereby being overlapped and rubbed with the sheet discharged from the feed roller group and the first roller group. Thus, an image on the sheet is rubbed, damaged or stained.